blockservice: async HasBlock with ratelimit

blockservice.go

@@ -8,6 +8,8 @@ import (
 	"fmt"
 
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
+	process "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/goprocess"
+	procrl "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/goprocess/ratelimit"
 	blocks "github.com/jbenet/go-ipfs/blocks"
 	"github.com/jbenet/go-ipfs/blocks/blockstore"
 	exchange "github.com/jbenet/go-ipfs/exchange"
@@ -17,6 +19,9 @@ import (
 var log = u.Logger("blockservice")
 var ErrNotFound = errors.New("blockservice: key not found")
 
+// MaxExchangeAddWorkers rate limits the number of exchange workers
+var MaxExchangeAddWorkers = 100
+
 // BlockService is a hybrid block datastore. It stores data in a local
 // datastore and may retrieve data from a remote Exchange.
 // It uses an internal `datastore.Datastore` instance to store values.
@@ -24,6 +29,9 @@ type BlockService struct {
 	// TODO don't expose underlying impl details
 	Blockstore blockstore.Blockstore
 	Exchange   exchange.Interface
+
+	rateLimiter *procrl.RateLimiter
+	exchangeAdd chan blocks.Block
 }
 
 // NewBlockService creates a BlockService with given datastore instance.
@@ -34,7 +42,17 @@ func New(bs blockstore.Blockstore, rem exchange.Interface) (*BlockService, error
 	if rem == nil {
 		log.Warning("blockservice running in local (offline) mode.")
 	}
-	return &BlockService{Blockstore: bs, Exchange: rem}, nil
+
+	// exchangeAdd is a channel for async workers to add to the exchange.
+	// 100 blocks buffer. not clear what this number should be
+	exchangeAdd := make(chan blocks.Block, 100)
+
+	return &BlockService{
+		Blockstore:  bs,
+		Exchange:    rem,
+		exchangeAdd: exchangeAdd,
+		rateLimiter: procrl.NewRateLimiter(process.Background(), MaxExchangeAddWorkers),
+	}, nil
 }
 
 // AddBlock adds a particular block to the service, Putting it into the datastore.
@@ -46,15 +64,21 @@ func (s *BlockService) AddBlock(b *blocks.Block) (u.Key, error) {
 		return k, err
 	}
 
-	// TODO this operation rate-limits blockservice operations, we should
-	// consider moving this to an sync process.
+	// this operation rate-limits blockservice operations, so it is
+	// now an async process.
 	if s.Exchange != nil {
+
+		// LimitedGo will spawn a goroutine but provide proper backpressure.
+		// it will not spawn the goroutine until the ratelimiter's work load
+		// is under the threshold.
+		s.rateLimiter.LimitedGo(func(worker process.Process) {
 			ctx := context.TODO()
 			if err := s.Exchange.HasBlock(ctx, b); err != nil {
 				// suppress error, as the client shouldn't care about bitswap.
 				// the client only cares about the blockstore.Put.
 				log.Errorf("Exchange.HasBlock error: %s", err)
 			}
+		})
 	}
 	return k, nil
 }